Response to chronic exposure to hexavalent chromium in human monocytes

Elevated circulating levels of metal ions, particularly chromium, have been measured in the blood of patients with metal hip implants, and this has lead to concerns about the long term safety of the prostheses. For example, depletion of lymphocytes has been reported in vivo in patients with metallic prostheses, and correlated with elevated chromium and cobalt concentrations in blood. However, the implications for immune function are unclear. We have assessed the in vitro responses of U937 human monocytes to chronic exposure (4 weeks) to Cr (VI) ions at concentrations which have been measured in patients with metal artificial hip implants (0.05-0.5 μM). Chronic exposure to these low clinically relevant concentrations of Cr (VI) induced a potent adaptive response with elevated glutathione-S-transferase (pi) expression and increased activities and expression of reactive oxygen scavengers, superoxide dismutases, catalase and glutathione peroxidase. Such direct toxicity of Cr ions may contribute to the effects of metal implants on lymphocyte populations in vivo.